The inventions generally relate to mobile/portable devices having displays.
For portable/mobile computing devices there are design tradeoffs that must be made relating to weight, size, battery life, etc. One significant tradeoff relates to the picture quality of a display vs. battery life. Good image display suggests the use of high voltages and clock rates to generate the high frequencies required. Preserving battery life suggests the use of lower voltages and clock rates. Typically, mobile computing devices designed for battery power will have its clocks and voltage set to the lowest possible values to conserve battery life. However, the lowest possible values are limited by various conditions including the need to maintain a flawless image on a display device.
Typically, image data is retrieved from memory that is clocked at a memory clock frequency (MCLK). Raw data retrieved from memory is converted one or more times before driving a display device. Such data conversions may include scaling, color space conversions, formatting, etc. Data conversions typically take place in a display block working at a system clock (SCLK) frequency. An image is displayed using a timing controller operating with a pixel clock (PCLK) frequency. If any one of these frequencies is below some necessary threshold level, visual artifacts caused by a display underflow will occur. A display underflow is a condition wherein a pixel required to be displayed is not present at a time when a display raster requires it.
A necessary pixel frequency is derived from timing requirements to support effective screen resolution. Calculation of other frequencies, especially memory clock, is more complex and less accurate. Typically production frequency values are determined during a comprehensive qualification process based on worst anticipated operational conditions. This does not prevent potential display underflow situations with emerging display devices, higher resolutions or more stressful applications that may require higher frequencies. On the other hand, frequencies chosen for the worst operational conditions are higher than necessary for most real life cases and the system therefore consumes more power, contributing to shorter battery life.
Display blocks of modern GPUs are capable to detect and signal underflow conditions, but this capability is used only for informational purposes during qualification. What is needed is a better way to preserve good image display without compromising battery life as much as it is compromised using typical techniques.